This invention relates to a method for forming for example an interlayer dielectric film of a semiconductor device, for example a film of carbon added fluorine (fluorine-added carbon).
In order to integrate semiconductor devices in higher density, various ideas have been proposed, for example, making patterns minute or multilayering circuits. As one of the ideas, there is known an art for multilayering wires. In order to achieve a multilayered wiring structure, an (n)-th wiring layer and an (n+1)-th wiring layer are connected with each other via an electric conducting layer. In addition, a thin film, which is called an interlayer dielectric film, is formed at an area or areas except the electric conducting layer.
An SiO2 film is a typical interlayer dielectric film. However, recently, it is required to lower a dielectric constant of the interlayer dielectric film in order to raise a speed of operation of the device further more. Then, characteristics of materials for the interlayer dielectric films are examined and studied. The SiO2 has a dielectric constant of about 4. Thus, various efforts have been made to find or form a material having a smaller dielectric constant. As one of the efforts, an SiOF film having a dielectric constant of 3.5 has been developed. However, inventors of this invention have paid attention to a film of flurorine-added carbon (hereafter, which is abbreviated as a CF film) having a further smaller dielectric constant.
Such a CF film is formed for example by using Argon (Ar) gas as a plasma gas, using a mixed gas including a compound gas of carbon (C) and fluorine (F) and a hydrocarbon gas as a film-forming gas, and making the film-forming gas into plasma in a plasma unit which can generate plasma for example by using electron cyclotron resonance. Then, the inventors have examined to use C6F6 (hexafluorobenzene) gas as the film-forming gas in order to raise thermal stability of the CF film.
If the CF film is used as an interlayer dielectric film, for example as shown in FIG. 10, a CF film 13 is accumulated on a SiO2 film 11 on which aluminum wires 12 are formed, so that gaps between the wires 12, 12 are filled up with the CF film 13. However, if C6F6 gas is used as the film-forming gas, since the C6F6 gas has a benzene ring i.e. a molecule of the C6F6 is large, as shown in FIG. 10(a), shoulder-like portions of the accumulated film above both side edges of a concave portion 14 between the wires 12,12 bulge out while the CF film 13 is accumulated. Then, the shoulder-like portions may contact with each other to block access to the concave portion 14. Thus, even if the concave portion 14 has an aspect ratio that is not so large, the concave portion 14 can not be filled with the CF film 13. That is, a or more large voids (spaces) 15 may be formed in the portion (see FIG. 10(b)).
This invention is intended to solve the above problem. The object of this invention is to provide a plasma film-forming method which can satisfactory fill up a concave portion with a CF film.
In order to achieve the object, a plasma film-forming method (a method of plasma-assisted film deposition) has a feature of comprising: a plasma-making step of making into plasma a film-forming gas including a compound of carbon and fluorine and an etching gas which can etch a film of fluorine-added carbon; and a film-forming step of forming a film of fluorine-added carbon onto an object to be processed by means of the plasma made in the plasma-making step.
According to the feature, if the CF film is used as an interlayer dielectric film, since the etching gas for etching the CF film is supplied in addition to the film-forming gas, a concave portion can be satisfactory filled up with the CF film.
The film-forming gas including a compound of carbon and fluorine includes for example a gas of a compound having a benzene ring, in particular hexafluorobenzene.
Preferably, the etching gas which can etch a film of fluorine-added carbon is a gas including fluorine, a gas including oxygen or a gas including hydrogen.
Preferably, hydrocarbon gas or a gas including silicon is supplied in addition to the film-forming gas and the etching gas, in the plasma-making step.